Enthalpy exchanger

ABSTRACT

A heat and humidity exchanger comprises panels made up of membrane sheets attached on either side of a separator. Channels extend across each panel between the separator and the membrane sheets. The panels are much stiffer than the membrane sheets. Panels are stacked in a spaced apart relationship to provide an ERV core. Spacing between adjacent panels may be smaller than a thickness of the panels.

FIELD

This invention relates to heat and humidity exchangers comprisingwater-permeable membranes. Example embodiments provide energy recoveryventilator (ERV) cores comprising water-permeable membranes and ERVsystems that include such cores. The invention may be applied in a widevariety of applications where heat and humidity exchange is required.Examples include heat and moisture (humidity) recovery in buildingventilation systems, humidification and heat transfer in fuel cells,separation of gases, and desalination treatment of water.

BACKGROUND

Heat and humidity exchangers (also sometimes referred to as humidifiers)have been developed for a variety of applications, including buildingventilation (HVAC), medical and respiratory applications, gas drying,and humidifying fuel cell reactants for electrical power generation.

Planar plate-type heat and humidity exchangers use membrane plates thatare generally constructed of flat, water-permeable membranes (forexample, Nafion®, cellulose, or other polymer membranes) supportedbetween separators. The plates are typically stacked, sealed andconfigured to accommodate intake and exhaust streams flowing in eithercross-flow or counter-flow configurations between alternate plate pairs,so that heat and humidity are transferred between the streams via themembrane.

A heat recovery ventilator (HRV) is a mechanical device thatincorporates a heat exchanger in a ventilation system for providingcontrolled ventilation into a building. The HRV heats or cools incomingfresh air using exhaust air. Devices that also exchange moisture betweenthe incoming fresh air and the exhaust air are generally referred to asEnergy Recovery Ventilators (ERVs), sometimes also referred to asEnthalpy Recovery Ventilators. An ERV may remove excess humidity fromthe ventilating air that is being brought into a building or it may addhumidity to the ventilating air. ERVs may be used to save energy and/orto improve indoor air quality in buildings.

The key component of an ERV system which transfers the heat and humiditybetween air streams, is the ERV core. Often ERV cores are constructedlike the planar plate-type heat and humidity exchangers described above.An ERV also typically comprises an enclosure, fans to move the airstreams, ducting, as well as filters, control electronics and othercomponents.

FIG. 1 shows an example of a planar plate-type heat and humidityexchanger made from stacked planar sheets of membrane 3 with rigidcorrugated separators 6 inserted between the membrane sheets. Theseparators support the membrane and maintain proper sheet spacing, aswell as defining channels 5 for wet and dry streams flowing on oppositesides of each membrane sheet, in a cross-flow arrangement, as indicatedby broad arrows 1 and 2 respectively. The membrane material is generallythin, flexible and not self-supporting. The separators 6 support themembrane, and reduce or prevent deflection of the membrane into thechannels 5. The stack is encased within a rigid frame 4. In some heatand humidity exchangers, plastic flow field inserts are used instead ofcorrugated separators to provide support for the membrane, maintainspacing and provide flow channels for the streams on either side of themembrane.

Examples of heat and humidity exchangers with corrugated separators aredescribed in US Patent Application Publication No. US2011/0192579.Examples of heat and humidity exchangers with flow field inserts aredescribed in U.S. Pat. Nos. 7,331,376 and 8,235,093.

Separators, such as corrugated members or flow field inserts that areused in the heat and humidity exchangers described above generallyprovide controlled or directional gas flow distribution over themembrane surface. However, the presence of such separators can restrictfluid flow across the membrane. The resulting pressure drop across theoverall apparatus can be significant. For example, even with parallel,straight channels if a separator provides many closely-spaced ribs tosupport the membrane, the ribs of any significant thickness will tend toimpede the fluid flow, and also increase pressure drop. The ribs mayalso block access of the fluid to a significant portion of the membranesurface. With more widely-spaced ribs the membrane can deflect into thechannel also increasing the pressure drop. In some cases, with flowfield inserts, the fluid flow path across the membrane can be quitetortuous which also tends to impede flow and increase pressure drop.Pressure drop is also induced by the increased wall surface areacreating drag or friction to the flow. Pressure drop can also beincreased as a result of deflection of the membrane into channelsprovided by the separators.

SUMMARY

This invention has a number of aspects. These aspects may be appliedindividually or in suitable combinations. Aspects of the inventioninclude, without limitation:

-   -   Humidity exchangers and heat and humidity exchangers;    -   Humidifiers for use in association with fuel cells and similar        devices;    -   Components for humidity exchangers and heat and humidity        exchangers;    -   Energy recovery ventilator (ERV) installations;    -   Methods for exchanging air between the interior and exterior of        a building;    -   Methods for making humidity exchangers, heat and humidity        exchangers, and/or parts for such exchangers; and    -   Fabrication apparatus useful for making humidity exchangers,        heat and humidity exchangers, and/or parts for such exchangers.

One example aspect of the invention provides a heat and humidityexchanger comprising a plurality of panels. Each of the panels comprisesa flexible separator formed to provide projections to either side of aplane of the separator and first and second thin water-vapor-permeablemembrane sheets attached to the projections on opposing faces of theseparator. The separator holds the first and secondwater-vapor-permeable membrane sheets in a spaced-apart parallelrelationship. The panel is stiffened by the attachment of the membranesheets to the separator. The projections are formed to provide firstchannels operable for carrying a first flow between the separator andthe first and second water-vapor-permeable sheets in a first directionacross each of the panels. The panels are stacked in a parallelspaced-apart relationship to provide open second channels betweenadjacent ones of the panels, the second channels extend to carry asecond flow through the heat and humidity exchanger in a seconddirection transverse to the first direction.

Advantageously the separator is corrugated or zig-zag in cross sectionsuch that the separator provides triangulated support to the membranesand the membranes stiffen the separator.

In some embodiments elongated spacers are provided between the adjacentones of the panels. The elongated spacers are spaced apart from oneanother in the first direction such that the second channels compriserelatively wide unobstructed openings. For example, the openings mayhave widths 20 times or more a thickness of the panels.

In some embodiments the panels are spaced apart from one another bydistances that are less than a thickness of the panels. For example, theseparators may have a depth that is in the range of 110% to 150%,preferably 125% to 135% of a height of the second channels. In someembodiments each of the panels has a thickness in the range of 1.5 mm to4 mm.

Portions of the separator to which the membranes are attached may beflattened. Such flattened areas may provide a greater area for adhesionbetween the membrane and separator. In the case where the separatorcomprises a corrugated sheet corrugations of the corrugated sheet may beformed to provide ridges having flattened tops. The membrane sheets maybe adhered to the separator along the flattened tops of the ridges.

In some embodiments the separator is perforated. The separator may, forexample, comprise a number of perforations that provide fluid connectionbetween some or all of the first channels in each panel.

In some embodiments the separator is of a material having a thickness of0.2 mm or less. For example, the separator may comprise a thin sheet ofmetal (e.g. aluminum) or plastic.

Vortex-generating features may optionally be provided in some or all ofthe channels of any embodiment described herein. An example embodimentcomprises plural vortex-generating features in at least the firstchannels or the second channels. The vortex-generating features maycomprise projections from and/or indentations into surfaces bounding thechannels. In some embodiments the vortex-generating features are formedon one or both of the first and second water-vapor-permeable membranesheets of a panel. In some embodiments a membrane sheet is embossed orformed to provide vortex-generating features that project on one face ofthe sheet and provide a corresponding recess on an opposing face of thesheet. In some embodiments a thickness of the membrane (or at least acoating of the membrane) is be similar of the same inside and outsidethe vortex-generating features formed in or on the membrane.

In some embodiments the vortex-generating features comprise an array ofprojections formed in a surface of the membrane, the projections havingheights of 1 mm or less or 2 mm or less. In some embodiments thevortex-generating features have heights not exceeding 2 mm or 40% of athickness of the separator, whichever is greater.

The first and/or second water-vapor-permeable membrane sheets in some orall of the panels are optionally asymmetrical. Asymmetrical membranesheets may comprise a substrate having an air-impermeable, water-vaporpermeable coating on one face of the substrate. The substrate may be airpermeable. For example, the substrate may comprise a porous (includingmicroporous) substrate. Where a membrane is asymmetrical the first andsecond water-vapor-permeable membrane sheets may be oriented such thatthe coatings face into the second channels.

Some embodiments provide one or more of the following features:

-   -   Edges of the panels extending parallel to the first channels are        tapered in thickness.    -   at flow rates through the first channels and the second channels        that are the same and are in the range of 35 to 95 SCFM pressure        drops across the first and second channels are the same to        within 25 Pa.    -   the first and second water-vapor-permeable membrane sheets are        affixed to the separator by an adhesive (which may comprise, for        example, a hot melt adhesive or a pressure sensitive adhesive.    -   The panels are spaced apart by spacer strips that may be solid        or hollow and of various cross-sectional configurations        including round, square, rectangular. In some embodiments the        spacer strips have thicknesses of at least 1.2 mm.

Another aspect of the invention provides an energy recovery ventilation(ERV) installation comprising a heat and humidity exchanger according toany described embodiment. The ERV installation may comprise an externalair intake connected to supply air from outside a building to aninterior of the building through the first channels or the secondchannels and external air outlet connected to deliver air from theinterior of the building to the exterior of the building by way of thesecond channels or the first channels. In some embodiments the interiorof the building is heated and the external air outlet is connected todeliver air from the interior of the building to the exterior of thebuilding by way of the second channels. In some embodiments the ERVinstallation is reconfigurable to switch which of the first and secondchannels is connected to the external air intake and which of the secondand first channels is connected to the external air outlet.

Another aspect of the invention comprises a panel for use in an ERV coreor a humidifier core. The panel comprises a separator formed to provideprojections to either side of a plane of the separator and first andsecond water-vapor-permeable membrane sheets attached to the projectionson opposing faces of the separator. The separator holds the first andsecond water-vapor-permeable membrane sheets in a spaced-apart parallelrelationship. The projections are formed to provide channels extendingacross each of the first and second water-vapor-permeable sheets betweenthe separator and the sheets.

Example embodiments provide one or more of the following features:

-   -   the separator is corrugated.    -   the separator is perforated.    -   the separator has a depth of less than 7 mm.    -   the separator is formed of a material having a thickness of 0.2        mm or less.    -   the separator comprises a formed aluminum sheet.    -   the first and second water-vapor-permeable membrane sheets are        affixed to the separator by an adhesive (which may, for example        comprise a hot melt adhesive or a pressure sensitive adhesive).    -   edges of the panel extending parallel to the channels are        tapered in thickness.

a plurality of spacer strips are attached to one of thewater-vapor-permeable sheets on a side opposite to the separator, thespacer strips extending in a direction generally perpendicular to thechannels. In some embodiments the spacer strips have thicknesses of atleast 1.2 mm. In some embodiments the spacer strips are separated fromone another by distances of at least 7 cm and/or at least 20 times athickness of the panel and/or at least 20 times a peak-to-peak spacingof the projections of the separator.

-   -   One or more of the first vapor-permeable sheet, the second        vapor-permeable sheet and the separator supports        vortex-generating features as described elsewhere herein.

Another aspect of the invention provides a method for making a heat andhumidity exchanger. The method comprises: forming a plurality of panelsby attaching first and second membrane sheets to opposing sides of aseparator formed to provide projections to either side of a plane of theseparator, the first and second membrane sheets attached to theprojections; and stacking the panels in a spaced-apart relationship withspacers separating the panels to provide channels between each pair ofadjacent panels. The panels may have any of the combinations of featuresas described elsewhere herein.

Another aspect of the invention provides apparatus having any new andinventive feature, combination of features, or sub-combination offeatures as described herein.

Another aspect of the invention provides methods having any new andinventive steps, acts, combination of steps and/or acts orsub-combination of steps and/or acts as described herein.

Further aspects and example embodiments are illustrated in theaccompanying drawings and/or described in the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate non-limiting example embodiments ofthe invention.

FIG. 1 is a perspective view of a conventional plate-type heat andhumidity exchanger.

FIG. 2 is an isometric view of a heat and humidity exchanger coreaccording to an example embodiment.

FIG. 2A is an expanded view showing a panel of the heat and humidityexchanger core of FIG. 2. FIG. 2B is a partially exploded view of an ERVcore. FIG. 2C is a cross-section view of a corrugated separator in aplane perpendicular to ridges of the corrugated separator. FIG. 2D is adiagram showing the depth and peak-to-peak spacing of a corrugatedmaterial. FIG. 2E is an expanded view showing a portion of the heat andhumidity exchanger core of FIG. 2.

FIGS. 2F, 2G, 2H and 2I show example profiles for a corrugatedseparator.

FIG. 2J is a cross section through a portion of an example panelcomprising a separator having a cross-sectional profile that includesridges with flattened tops.

FIG. 2K is a perspective view of a portion of a membrane provided withvortex-generating features.

FIG. 3 is a flow chart illustrating a method for making a heat andhumidity exchanger core according to one embodiment.

FIG. 4 illustrates an example production line for the manufacture ofheat and humidity exchanger cores according to an example embodiment.

FIG. 5A, illustrates a laminated material ready to be cut into panelsaccording to certain example embodiments.

FIG. 5B is a blown-up view of a section of a laminated material likethat shown in FIG. 5A showing a first step in forming a panel edge. FIG.5C is a blown-up view of a section of a laminated material like thatshown in FIG. 5A showing a second step in forming a panel edge

DETAILED DESCRIPTION

Throughout the following description, specific details are set forth inorder to provide a more thorough understanding of the invention.However, the invention may be practiced without these particulars. Inother instances, well-known elements have not been shown or described indetail to avoid unnecessarily obscuring the invention. Accordingly, thespecification and drawings are to be regarded in an illustrative, ratherthan a restrictive sense.

FIG. 2 is a perspective view of a heat and humidity exchanger core 10according to an example embodiment. Core 10 comprises a plurality ofpanels 12 that are stacked together in a spaced apart relationship.Separation between adjacent panels 12 is maintained by spacers 14.

Each panel 12 comprises first and second membrane sheets 12A and 12Bthat are attached on either side of a corrugated member 12C. Each ofmembrane sheets 12A and 12B and corrugated member 12C may beindividually flexible. However, attachment of membrane sheets 12A and12B to corrugated member 12C results in a panel which is relatively verystiff. One measure of stiffness is the amount of deflection that resultsfrom application of a concentrated load. One way to measure stiffness ofpanels 12 is provided by TAPPI Standard T836.

Membrane sheets 12A and 12B are permeable to water vapor to enableexchange of humidity between a flow of air or other gas in channels 12Dinternal to panel 12 and air or other gas flowing outside of panel 12adjacent to the corresponding membrane sheet 12A or 12B. Membranes 12Aand 12B may be substantially air impermeable. In example embodiments,one or both of membrane sheets 12A and 12B comprises a composite polymermembrane with porous substrate and selectively water vapor permeablecoating. The coating is preferably selective for water vapor (i.e. has asignificantly higher permeability to water vapor than to other gaseswhich are desired not to pass through the coating). Examples of somesuitable membrane materials are described, for example, in US PatentApplication Publication No. US2012/0061045, and U.S. Pat. No. 8,936,668.

Membrane sheets 12A and 12B may be thin, flexible and notself-supporting when not assembled into and supported by panels 12.Membrane sheets 12A and 12B may comprise commercially-available watervapor exchange membranes. Membrane sheets 12A and 12B may becharacterized by some or all of:

-   -   High water permeation (vapor and liquid);    -   High water absorption;    -   Low or zero air and contaminant gas permeation;    -   Non-flammability;    -   Resistance to microbial growth;    -   Long lifetime under the required operating conditions, without        detrimental leaching or loss of membrane components and without        significant degradation in water vapor transport performance or        increased contaminant crossover;    -   Tolerance to freeze-thaw cycles in the presence of liquid water        condensation without significant deterioration in performance;    -   Low cost.        Some example membrane sheets have thicknesses in the range of 5        to 250 microns. In some embodiments the membrane sheets are more        flexible in one direction than in a perpendicular direction.        Such membrane sheets may be oriented so that the direction in        which the sheet is stiffest is transverse to ridges of separator        12C.

In example embodiments, membrane sheets 12A and 12B are each adhesivelyaffixed or otherwise attached to ridges of corrugated member 12C.Attachment may be continuous along each of the ridges or interruptedalong some or all of the ridges. In some embodiments, attachment iscontinuous along one or more outermost ridges on each side of a panel 12and is interrupted along ridges internal to panel 12. Even if adhesiveis distributed only intermittently along some ridges, the adhesive mayextend continuously along the outermost ridges on either edge of eachsheet 12A or 12B. This construction seals along these edges. In someembodiments, the adhesive is a hot melt adhesive.

In some embodiments, sheets 12A and 12B are caused to shrink afterbonding to separator 12C such that sheets 12A and 12B are taut and donot sag between their points or regions of attachment to separator 12C.Shrinkage may occur through, for example, relaxation of tensile stresses(if the membrane is pre-tensioned) or cooling post-lamination (thermalcontraction).

FIG. 2A shows an example panel 12 equipped with spacers 14 forseparating the panel from an adjacent panel.

FIG. 2B shows an ERV core made up of a plurality of panels 12 of thegeneral type shown in FIG. 2A stacked together. FIGS. 2C and 2Dillustrate a corrugated separator showing dimensions referred to hereinas the peak-to-peak spacing and the depth.

Separator 12C is preferably made of a material or materials differentfrom membrane sheets 12A and 12B. In some embodiments, separator 12Ccomprises a corrugated member formed from a sheet of a formable metalsuch as aluminum. Such embodiments have the advantage that corrugatedmembers 12C are non-flammable. In other embodiments, separator 12C maycomprise a plastic sheet. In some embodiments, the peak-to-peak spacingof corrugations (as defined in FIG. 2D) is in the range of about 4 mm or5 mm to 15 mm. In an example embodiment, the peak-to-peak spacing isabout 7 mm.

Separator 12C may have but does not necessarily have corrugations thatare zig-zag or sinusoidal or approximately so. In some embodiments, theridges of separator 12C are narrow in comparison to a sinusoid of thesame peak-to-peak spacing. FIGS. 2F, 2G, 2H and 2I show non-limitingalternative example cross-sectional shapes for a separator 12C.

In some embodiments separator 12C has a profile that provides ridgeshaving flattened tops. Flattened tops provide surfaces that may supportstrong adhesive bonds between the membranes and separator 12C. FIG. 2Jis a cross-sectional view of an example separator 12C-1 that exhibits anoverall cross-sectional profile that is a zig-zag profile with flat ornearly flat sections 112 that connect flattened-topped ridges 113. Whenassembled into a panel, with membrane sheets 114 attached at ridges 113,flat sections 112 provide triangulated support for the membrane sheets.A flattened surface of a ridge may provide a foundation for goodattachment of adhesive 115 to separator 12C. Additionally, providingridges with flattened tops may help to reduce pressure drop acrosschannels 12D by avoiding narrow corners in the valleys 116 correspondingto ridges 113. The flattened tops may be kept fairly narrow to keep thearea of membrane sheets 114 occluded by flattened-topped ridges 113relatively small compared to the overall area of membrane sheets 114.

In some embodiments, separator 12C is perforated. Perforations may be ofany suitable shape or shapes. Optionally the perforations are confinedto walls of the separator which separate adjacent channels 12D.

The material from which separator 12C is formed may be thin. A separator12C provided by a thin corrugated member may provide reduced pressuredrops across channels 12D in comparison to a thicker corrugated member.In some embodiments, separator 12C is of a material having a thicknessin the range of 0.001 in (about 0.025 mm) to 0.008 in (about 0.2 mm). Insome embodiments separator 12C is of a material having a thickness of0.2 mm or less.

In core 10 a plurality of panels 12 are stacked and spaced apart fromone another by spacers 14. Spacers 14 may, for example, have the form ofstrips, rods, ribs or bars. Spacers 14 may, for example, comprise stripsof plastic, aluminum, or another suitable separator material.

Spacers 14 need not be solid but may optionally be hollow. In someembodiments, spacers 14 are circular in cross-section. Spacers 14 thatare circular in cross section can be advantageous because they do notrequire any particular orientation. Also, if circular spacers rotateduring or after placement, the rotation does not change the spacingbetween adjacent panels 12.

Spacers 14 are dimensioned to provide channels 15 between adjacentpanels 12. Heat and humidity are exchanged between gases in channels 15and gases in the channels 12D internal to adjacent panels 12.

Ends of core 10 may be closed off by end panels 11 of any suitablematerial.

Spacers 14 advantageously extend continuously across panels 12. In somealternative embodiments some of spacers 14 may not extend all of the wayacross panels 12. For example, in some embodiments a number of shorterspacers 14 arranged end-to end are provided in place of one of theillustrated spacers 14. Ends of the shorter spacers 14 may abut oneanother or may be spaced apart.

In preferred embodiments, spacers 14 are oriented generallyperpendicularly to the ridges of corrugated members 12C. Spacers 14 maybe configured to block flow in a direction transverse to spacers 14.

Two spacers 14 may be arranged to extend along opposing edges of twoadjacent panels 12. In such embodiments, the outmost spacers 14 mayserve the additional function of sealing the edges of channels 15. Oneor more additional spacers 14 may optionally be spaced apart acrosspanels 12. For example, a spacer 14 may be provided approximately every50 to 200 mm. It is not mandatory that all of spacers 14 be equallyspaced apart from neighboring spacers 14.

Spacers 14 defining different channels 15 may be aligned so that theyare parallel with one another. In some embodiments, channels 15 areunobstructed between spacers 14 and adjacent spacers 14 are separated bydistances that are one or more of:

-   -   at least 7 cm;    -   at least 20 times a thickness of panels 12;    -   at least 20 times a peak-to-peak spacing of the corrugations of        layer 12C of panels 12.

As illustrated in FIG. 2E, the spacing between adjacent panels 12 maydiffer from the thicknesses of individual panels 12. In particular, insome embodiments, adjacent panels 12 are spaced apart by distances D2that are smaller than the depth D1 of corrugated members 12C which alsodefines the spacing between inner faces of sheets 12A and 12B in eachpanel 12. This result may be achieved by making spacers 14 thinner thanthe distance D1 between sheets 12A and 12B of one panel 12.

In some embodiments, the spacing D2 between adjacent ones of panels 12is selected such that the pressure drop across channels 15 and thepressure drop across channels 12D for the same flow rate is at leastapproximately equal, at least when the flow rate is such that the flowconditions are dominated by laminar flows in channels 12D and 15.

In some embodiments, the depth D1 of separator 12C is in the range of110% to 150% or preferably 120% to 135% of the height of channels 15(which is shown as D2 in FIG. 2E). In an example embodiment, depth D1 ofseparator 12C is about 2.6 mm while the height (D2) of channels 15 isabout 2 mm.

In some embodiments channels 15 and 12D are configured so that thepressure drop across channels 15 and 12D is the same to within 25 Pa atflow rates through the channels that are the same and are in the rangeof 35 to 95 SCFM (these flow rates might be experienced in a typicalresidential ERV core). In some embodiments when laminar flow ismaintained through channels 15 and 12D so that the total flow throughall channels 15 is the same as the total flow through all channels 12D,the pressure differential across membrane sheets 12A and 12B iseverywhere less than twice the pressure drop across each set of channels(12D and 15).

In another example characteristic of some embodiments, the depth D1 ofseparator 12C (which is also the spacing between inner faces of sheets12A and 12B in a panel 12) is in the range of about 1.6 mm to 7 mm.Depth D1 may be more than the spacing D2 between outer faces of sheets12A and 12B on either side of a channel 15 (typically 110% to 150% morethan D2). D2 is typically in the range of about 1.3 mm to about 5.5 mm.

In some embodiments the lateral dimensions (i.e. length and width) ofpanels 12 are also selected to provide a desired pressure drop acrosschannels 12D and 15. For example, if the dimensions D1 and D2 are thesame, there will tend to be a greater pressure drop across channels 12Dthan channels 15, for a given flow rate (because separator 12C causessome resistance to fluid flow). If it is desired to balance the pressuredrop then, instead of, or in addition to, selecting a value of D2relative to D1, the relative lengths of channels 15 and 12D may beadjusted to balance the pressure drops. For example, for the case wherethe pressure drop per unit length of channels 12D is greater than thatfor channels 15, channels 15 may be increased in length relative tochannels 12D. For example, channels 15 can be made to have lengthsgreater than that of channels 12D by using rectangular (rather thansquare) panels 12. Channels 12D may extend across the shorter dimensionof panels 12 and channels 15 may extend across the longer dimension ofpanels 12.

Another design feature that may be used to balance the pressure dropacross channels 12D and 15 is the inclusion of vortex-generatingfeatures arranged to disrupt laminar flow and/or increase turbulence inone of both of channels 12D and 15. The presence of such features in achannel can increase pressure drop across the channel for a given flowrate. For example, the height (e.g. D1 or D2) of a channel may beincreased and/or the length of the channel may be decreased withoutdecreasing pressure drop across the channel if suitablevortex-generating features are added to the channel to compensate forthe change in channel height or length.

In some embodiments, membranes 12A and 12B each comprise a substratethat supports a layer of a water vapor selective material. In someembodiments, the substrate is a macroporous substrate while the layer isa water vapor selective material formed as a thin dense or continuousfilm on one face of the macroporous substrate.

In some embodiments, the membranes are oriented such that the coatedside of the membrane (i.e. the side of the membrane that carries thewater vapor selective material) faces away from separators 12C. In someembodiments, the membranes are oriented such that the coated side of themembrane (i.e. the side of the membrane that carries the water vaporselective material) faces toward separators 12C. In some embodiments,the membranes are oriented such that the coated side of the membrane(i.e. the side of the membrane that carries the water vapor selectivematerial) faces away from separators 12C. In some embodiments, themembrane adjacent one side of the corrugated member is oriented suchthat the coated side of the membrane (i.e. the side of the membrane thatcarries the water vapor selective material) faces away from separator12C and the membranes adjacent the other side of the separator 12C isoriented such that the coated side of the membrane faces toward theseparator 12C.

Particular orientations of an asymmetric membrane (such as a membranewith a coating on one side) may offer advantages in certain applicationsof the heat and humidity exchangers described herein. Some factors whichmay guide the choice of which way to orient asymmetric membranes inpanels 12 on either side of corresponding separators 12C include:

-   -   Whether the adhesive or bonding mechanism used to attach the        membranes to one or the other of the corrugated separator 12C or        spacers 14 adheres better to the coated or uncoated side of the        membrane.    -   For some coatings, optimum performance can be achieved by        orienting the membrane such that the coating faces toward the        more humid stream.    -   Some membrane coatings may have a permeability to moisture that        is temperature-dependent. For example, the vapor-permeability of        a membrane coating may increase with temperature. This property        may be exploited by orienting the membrane so that the coated        side of the membrane faces the warmer stream (which is typically        also the more-humid stream).    -   Industry standards for the effectiveness of ERV installations        require greater latent effectiveness for cooling applications        than for warming applications. In ERV installations located in        regions having climates where the ERV will be used in both        warming (usually winter) and cooling (usually summer) conditions        the membranes may be oriented such that the coated side of the        membrane faces the stream that is more-humid during warming        conditions so as to provide increased latent effectiveness in        the cooling conditions.    -   In cases where cold air is directed through channels 12D so that        condensation may occur in open channel 15, the membrane(s)        bounding open channel 15 may be oriented with the coated side        facing open channel 15 to facilitate draining of liquid water        from channels 15 and to facilitate defrosting or ice melting.

One advantage of some embodiments is that the relatively unobstructedchannels 15 present reduced resistance to gas flow. Furthermore, underpotential icing conditions unobstructed channels are much less likely tobecome obstructed by the buildup of frost or ice than small individualchannels as are present in some prior art heat and humidity exchangerdesigns. This is partly because there are fewer walls against whichfrost can build up. In some constructions frost may form on impermeablewalls of a separator. With small channels, once one of the channelsbecomes partially obstructed by ice, the fluid will tend to by-pass thatchannel which then will increase the tendency for the channel to becomecompletely blocked. The materials used (such as for the separators,membrane coating or spacers) may be selected to be hydrophobic or changethe surface tension to allow condensation to better drain and improvefrost inhibition.

In some embodiments, lateral edges of panels 12 are tapered in thicknessso as to provide tapered lead-ins and/or lead-outs to channels 15. Thisconstruction can further reduce pressure drops across channels 15.

In some embodiments tapered lead ins are also provided for channels 12D.For example, outermost spacers 14 may have tapered portions that projectoutwardly past openings of channels 12D and thereby provide taperedlead-ins and/or lead-outs to channels 12D. This construction can furtherreduce pressure drops across channels 12D.

In some embodiments vortex-generating features are provided to increaseturbulence in the flow within channels 12D and/or 15. Where a flow ofgas (e.g. moist air) in the channels has some flow separation a degreeof turbulence can cause mixing that allows different portions of the gasto be brought into contact with the membrane as the gas flows throughthe channel. Vortex generating features may comprise small projectionsand/or recesses formed in one or more of the surfaces that bound thechannels. For example, in some embodiments vortex-generating featuresmay be provided by embossing one or both layers of membrane in a panelto provide concavities and/or convexities facing channels 12D and/or 15.

Vortex-generating features may be arranged to modify the flow fieldinside the channels at a desired flow rate, to increase heat andmoisture transfer without causing an excessive increase in pressure drop(energy loss in the flow due to fluid friction and drag) across thechannels. In some embodiments vortex-generating features are formed intoa separator 12C and/or spacers 14 in addition to, or instead of, formingthe vortex-generating features in the membranes. For example, thematerial of a separator 12C may be formed to provide projections,apertures, flaps or recesses in walls of channels 12D and/or projectionsand/or indentations may be provided along edges of spacers 14.

In addition to providing improved contact between the membrane and theair flowing in the channels bounded by the membrane, vortex generatingfeatures may be used in combination with other design features tobalance pressure drop across channels 12D with pressure drop acrosschannels 15.

Vortex-generating features may have any of a wide variety ofconfigurations. For example, such features may comprise smalltetrahedral, rectangular, square, irregular or peg-like projections froma surface bounding one of the channels. Such features may be presentedas a regular array or an irregular array. In some embodiments, suchfeatures are provided more densely at an inlet end of a channel and arereduced or absent in a portion toward an outlet end of the channel.

In some embodiments, the vortex-generating features have dimensions onthe order of 1 mm. For example, such features project from a surface bya distance in the range of ⅛ mm to 2.5 mm in some embodiments. Suchfeatures have a width in a direction transverse to the channel in therange of ⅛ mm to 5 mm in some embodiments. In some embodiments some orall of the features are elongated in a direction that is generallyparallel to the longitudinal axis of the channel.

FIG. 2K shows a portion of a membrane 12A that is embossed withvortex-generating features in the form of an array of rectangularprojections 17. In an example embodiment, the projections have a lengthof about 7.5 mm, a width of about 0.6 mm and a height of about 0.65 mm.The opposing face of membrane 12A may be patterned with indentationscorresponding to each of features 17.

FIG. 3 is a flow chart illustrating a method 30 providing a sequence ofsteps that may be applied to make a heat and humidity exchanger coreaccording to an embodiment of the invention. In some embodiments of themethod the steps may be performed in a different sequence, and/or someof the steps may be omitted and/or there may be additional stepsinvolved.

In block 31, sheets of membrane are supplied. The sheets of membranemay, for example, be supplied in the form of rolls having widths equalto one dimension of panel 12. In block 32, a separator sheet material isprovided. The separator sheet material may also, for example, beprovided in a roll of material. The width of the separator sheetmaterial provided in block 32 may be substantially equal to the width ofthe membrane sheets provided in block 31.

In block 33, the separator sheet material is corrugated, for example byforming between patterned (e.g. toothed) rolls or pressing.

In block 34, adhesive is applied along ridges of the corrugatedseparator sheet. The adhesive may, for example, comprise a hot meltadhesive or pressure sensitive adhesive. In some embodiments theadhesive is applied by adhesive-coated rollers that contact the ridgesof the corrugated separator sheet and/or by nozzles that eject drops,beads or ribbons of adhesive onto the ridges of the corrugated separatorsheet.

In block 35, the membrane sheets are adhered on either side of thecorrugated separator sheet to form a laminated material. In someembodiments, the membrane sheets are applied simultaneously to theopposed faces of the corrugated separator sheet. Such embodiments, inwhich the membrane sheets are affixed substantially simultaneously atdiametrically-opposed locations on opposing faces of the corrugatedspacer sheet, may be advantageous for enhancing overall flatness of thepanels and/or reducing any tendency of the membrane to sag. In someembodiments, one of the membrane sheets is applied to one face of thecorrugated separator sheet before the other membrane sheet is applied toan opposing area on the other face of the corrugated separator sheet.

Block 36 provides spacers (e.g. spacers 14). The spacers may be suppliedalready cut to a desired length or may be also drawn from a roll, or maybe cut to length from longer pieces or may be extruded directly onto themembrane. In block 37, the spacers are bonded at desired locations toone of the membrane sheets. In block 38, panels are cut from thelaminated material. Blocks 37 and 38 could be performed in either order(i.e. spacers 14 could be applied before or after individual panels 12are formed).

Spacers may, for example, be applied to panels 12 by extruding thespacers on to the panels 12, gluing the spacers into place, attachingthe spacers adhesively or the like. In some embodiments, spacers 14 maybe applied as a settable material such as a liquid, paste or gel. Insuch embodiments, a temporary spacing member may be applied to separateadjacent panels 12 by a desired spacing. The temporary spacing membermay be removed after the settable material has hardened sufficiently tomaintain the desired spacing.

In some embodiments, block 38 comprises removing the membrane from oneside of the laminated material between two ridges of the corrugatedseparator. Removal of the membrane may, for example, comprise lasercutting, cutting with a heated ribbon, cutting with a movable blade etc.Cutting the panels may further comprise a step of cutting through thecorrugated member and the opposing membrane at a point where thecorrugated member is affixed to the opposing membrane as indicated inblock 38B.

In block 39, the resulting panels are stacked. In block 40 the spacerspreviously attached to a membrane on one side of the panels are bondedto an adjacent panel in the stack.

When the desired number of panels have been assembled into the stack,the core is completed and may be ejected from the apparatus. The methodoptionally includes additional steps such as the application of seals ora frame etc.

FIG. 4 shows apparatus 50 according to an example embodiment formanufacturing ERV cores 10. Apparatus 50 employs rolls of membranematerial 51A and 51B and a roll of separator material 51C. Separatormaterial, for example, aluminum foil, passes between corrugating rollers52. Adhesive applicator 53 applies adhesive to ridges of the corrugatedseparator material. Adhesive applicator 53 may, for example, comprise anadhesive-coated roller.

In some embodiments of the apparatus the corrugation depth (e.g. D1 inFIG. 2E) is readily and conveniently adjustable. In the illustratedembodiment the separator material is corrugated perpendicular to thedirection of movement of the materials through rollers 52. Otherembodiments may form corrugations extending in another direction (e.g.parallel to the direction of movement).

Sheets of membrane from rolls 51A and 51B are brought together on eitherside of the corrugated separator material at rollers 54 which bond themembrane to the separator material to form a laminated material.

The corrugated separator material is optionally compressed slightly in adirection perpendicular to the corrugations prior to bonding, so thatthe membrane will be stretched or held in tension after it is bonded tothe separator material. After rollers 54, the membranes and theseparator sheet form a laminated material with membrane sheets bonded toeither side of the corrugated separator sheet. Spacer strips are fedfrom a roll 55 of strip material. Adhesive is applied to each spacerstrip by an adhesive applicator 58. Spacer strips are bonded to one sideof the laminated material at rollers 59. In other embodiments, thespacer strips can be extruded directly on to the membrane. For examplespacer strips may be made from a melt-processable plastic and may beextruded onto the laminated material.

A cutting device 60 such as, for example, a shear or laser cutter cutsthe laminated material into panels 12. An adhesive applicator 62 appliesadhesive to the spacers 14 on each panel 12. At stacker 65, the panels12 are stacked on top of one another and bonded together.

In some embodiments, edges of panels 12 are cut to provide a taperedlead-in to channels 15. One way to achieve this is illustrated in FIGS.5A to 5C. In such embodiments, membrane 12A may be cut close to a pointat which it is adhered to an outermost ridge on one side of panel 12 andmembrane 12B may similarly be cut at a location close to the point wheremembrane 12B is affixed to an outermost ridge on the other side of panel12. This exposes an angled face 12E of corrugated member 12C. Suchtapered edges may optionally but preferably be formed along both opposededges of a panel 12. Each of these opposed tapered edges smooth the flowof air or other gas into and out of channels 15.

In some embodiments, panels 12 are stacked and held together by a framecomprising corner members 18 (see FIG. 2). Corner members 18 compriseL-shaped members in some embodiments.

The construction described herein may be altered to make ERV cores ofmany configurations. For example, panels 12 may be square but may alsohave other shapes (e.g. rectangular or even rounded shapes).

In some embodiments, membrane sheets 12A and 12B and corrugated member12C are made of a material compatible with non-adhesive bondingprocesses. For example, a substrate of membrane sheets 12A and 12B maycomprise a plastic material that can be bonded to a plastic material ofcorrugated member 12C by a welding process (e.g. laser welding orultrasonic welding or thermal welding). Similarly, in some embodiments,spacers 14 are made of a material compatible with non-adhesive bondingprocesses.

In some embodiments, corrugated member 12C is replaced with a memberthat is stamped or otherwise formed to provide projections such asdimples, ridges or bumps externally to either side which support sheets12A and 12B in a spaced-apart parallel relationship and which, whenattached to sheets 12A and 12B yield a relatively stiff self-supportingpanel 12.

Cores as described herein may be integrated into a heat and humidityexchanger system which includes first plenums connected to bring flowsof air to and from channels 15, second plenums connected to bring flowsof air to and from channels 12D and blowers connected to maintain equaltotal flow volumes through channels 15 and 12D. The heat and humidityexchanger system may be constructed to provide even flow distributionacross each of channels 15. The heat and humidity exchanger system maybe constructed to provide even distribution of flow among channels 12D.

In some embodiments a heat and humidity exchanger is arranged so thatwarmer, more humid air being exhausted from a building in winter iscarried in channels 15 which are more open and therefore more likely toavoid frost formation than channels 12D. This arrangement may permitoperation at lower outside temperatures.

In some embodiments, coatings on membrane sheets 12A and 12B arearranged to face outside air being drawn into a building. Thisarrangement can improve latent heat transfer in the summer (whenincoming outside air is relatively hot and humid as compared to coolerair conditioned air being exhausted from the building).

In some applications it is desirable to run a heat and humidityexchanger so as to carry more flow (higher mass transport) in onedirection than in another. For example, in a commercial application itmay be desirable to provide more flow on a supply side (fresh airentering a structure) than on an exhaust side (air exiting the structureby way of the heat and humidity exchanger). This may be done to maintaina positive pressure inside the structure and/or to make up for airescaping through doors, windows or other leakage pathways or when somereturn air is not distributed back to the ERV system. In such cases itmay be beneficial to use channels 15 as the supply side. If channels 15are operating at a pressure slightly higher than channels 12D, theresulting forces on panels 12 will tend to compress panels 12.

It would be desirable to provide ERV cores and other heat and/or vaporexchangers that include channels that carry flow of air or other gas tobe dehumidified or humidified are wide and open. For example, twoparallel flat membranes defining an entirely open channel between themwould be beneficial. Due to limitations in the rigidity of the thinwater-vapor permeable membranes, this is not generally possible. In heatand mass transfer theory validated empirically, a channel geometry moreclosely approaching a circle will provide higher heat and mass transferfor laminar flow given by the Nusselt number. Therefore, an open channelincreases mass transfer coefficients relative to a triangular channel,since diffusion and convective transfer in the third dimension isaffected by the shape of the channel. Likewise, the Nusselt number fortwo parallel flat plates corresponds to increased mass transfercoefficients relative to a square channel

Non-limiting example constructions for heat and vapor exchangers basedon the foregoing teachings include:

-   -   An ERV installation for use in warm and humid climates, such as        in the southern United States may be constructed such that        more-humid, warmer air flows into an air-conditioned building        through one set of channels 12D or 15 and cooler, less-humid air        flows out of the building through the other one of channels 15        and 12D. In such installations it can be advantageous to orient        a membrane such that the coated side of the membrane is        preferably oriented such that the coating faces the more-humid        incoming air. This generally allows for the higher transfer of        water vapor that is to be removed from the incoming stream        (dehumidification). Vortex generators may optionally be provided        to cause turbulence in the incoming more-humid and hotter        stream, to enhance contact between water vapor being carried in        the incoming air and the surface of the membrane. In this        application, an example typical spacing between adjacent plates        12 is in the range of 1.5 mm to 5 mm, to allow for high flow        rates and low pressure drop, or increased heat and mass        transfer.    -   An ERV installation in a residential unit located where the        climate is cold, such as in Canada or the northeast United        States may be constructed so that colder, less-humid air flows        into a heated building through one set of channels 12D or 15 and        warmer, more-humid air flows out of the building through the        other set of channels 15 and 12D. Such an installation may be        arranged to reduce the tendency for formation of frost in the        channels carrying more-humid air and to facilitate drainage of        condensate that may form in the channels. In such applications        it is generally advantageous to allow outgoing warmer,        more-humid air to flow through open channels 15. This can allow        warm air to more-easily reach frost locations in the core, and        can also facilitate drainage of condensate from channels 15. In        some embodiments channels 15 are oriented such that the        membranes bounding channels 15 are non-horizontal (e.g. vertical        or tilted to facilitate gravity-assisted drainage of        condensate). Vortex generators, if provided, are preferably        provided on the dry supply side (i.e. in channels 12D). This        reduces the possibility that vortex generators could make frost        formation more likely, or serve as sites for nucleation of        liquid water. For higher water vapor transfer, the membranes may        be oriented such that a coated side of the membrane faces the        more-humid outgoing stream.    -   In some regions an ERV may function for one part of the year to        bring warm moist air into a building and to allow cool drier air        to exit the building, and for another part of the year to bring        cold dry air into the building and to expel heated more-humid        air from the building. Some ERV installations are reconfigurable        to selectively allow intake air to pass through channels 12D or        15 and to allow air being expelled from the building to pass        through the other set of channels 15, 12D. This allows the ERV        installation to be configured, as described above, to suit        either part of the year.    -   A water vapor exchanger or humidifier, for an example automotive        fuel cell application, may have pitches in the range of 0.3 mm        to 1.5 mm, for example. In such applications it is often        desirable that sizes of plates 12 are typically 200 mm or less        in width or length. Separator strips in channels 15 may, for        example, be spaced apart by distances in the range of about 30        mm to about 100 mm.

In addition to a heat and humidity exchanger as described herein An ERVinstallation may include ductwork for bringing outside air into abuilding by way of the heat and humidity exchanger and carrying insideair out of the building by way of the heat and humidity exchanger, oneor more blowers for driving air flow in one or both directions and acontrol system. In some embodiment the control system includes sensorsfor some or all of air temperature at one or more locations, airmoisture content at one or more locations, liquid water at one or morelocations air pressure drop across one or both sides of the heat andhumidity exchanger air flow through the heat and humidity exchanger andthe like. In response to inputs from the sensors the controller may takeaction such as regulating air flow into and/or out of the building,defrosting the heat and humidity exchanger or the like.

Interpretation of Terms

Unless the context clearly requires otherwise, throughout thedescription and the

-   -   “comprise”, “comprising”, and the like are to be construed in an        inclusive sense, as opposed to an exclusive or exhaustive sense;        that is to say, in the sense of “including, but not limited to”;    -   “connected”, “coupled”, or any variant thereof, means any        connection or coupling, either direct or indirect, between two        or more elements; the coupling or connection between the        elements can be physical, logical, or a combination thereof;    -   “herein”, “above”, “below”, and words of similar import, when        used to describe this specification, shall refer to this        specification as a whole, and not to any particular portions of        this specification;    -   “or”, in reference to a list of two or more items, covers all of        the following interpretations of the word: any of the items in        the list, all of the items in the list, and any combination of        the items in the list;    -   the singular forms “a”, “an”, and “the” also include the meaning        of any appropriate plural forms.

Words that indicate directions such as “vertical”, “transverse”,“horizontal”, “upward”, “downward”, “forward”, “backward”, “inward”,“outward”, “vertical”, “transverse”, “left”, “right”, “front”, “back”,“top”, “bottom”, “below”, “above”, “under”, and the like, used in thisdescription and any accompanying claims (where present), depend on thespecific orientation of the apparatus described and illustrated. Thesubject matter described herein may assume various alternativeorientations. Accordingly, these directional terms are not strictlydefined and should not be interpreted narrowly.

Methods as described herein may be varied in a range of ways. Forexample, while processes or blocks are presented in a given order,alternative examples may perform routines having steps, or employsystems having blocks, in a different order, and some processes orblocks may be deleted, moved, added, subdivided, combined, and/ormodified to provide alternative or sub-combinations. Each of theseprocesses or blocks may be implemented in a variety of different ways.In addition, while processes or blocks are at times shown as beingperformed sequentially, they may instead be performed simultaneously orin different sequences. It is therefore intended that the followingclaims are interpreted to include all such variations as are withintheir intended scope.

Where a component (e.g. frame, fan, membrane, panel, etc.) is referredto above, unless otherwise indicated, reference to that component(including a reference to a “means”) should be interpreted as includingas equivalents of that component any component which performs thefunction of the described component (i.e., that is functionallyequivalent), including components which are not structurally equivalentto the disclosed structure which performs the function in theillustrated exemplary embodiments of the invention.

Where this disclosure indicates that a feature is provided “in someembodiments” or in “example embodiments” that feature may optionally beprovided an any other described embodiment as long as the feature is notincompatible with the other described embodiment. The feature may beprovided on its own or in any combination with other features.

Specific examples of systems, methods and apparatus have been describedherein for purposes of illustration. These are only examples. Thetechnology provided herein can be applied to systems other than theexample systems described above. Many alterations, modifications,additions, omissions, and permutations are possible within the practiceof this invention. This invention includes variations on describedembodiments that would be apparent to the skilled addressee, includingvariations obtained by: replacing features, elements and/or acts withequivalent features, elements and/or acts; mixing and matching offeatures, elements and/or acts from different embodiments; combiningfeatures, elements and/or acts from embodiments as described herein withfeatures, elements and/or acts of other technology; and/or omittingcombining features, elements and/or acts from described embodiments.

It is therefore intended that the following appended claims and claimshereafter introduced are interpreted to include all such modifications,permutations, additions, omissions, and sub-combinations as mayreasonably be inferred. The scope of the claims should not be limited bythe preferred embodiments set forth in the examples, but should be giventhe broadest interpretation consistent with the description as a whole.

What is claimed is:
 1. A heat and moisture exchanger comprising: aplurality of panels, each of the panels comprising a flexible separatorformed to provide projections to either side of a plane of theseparator; and first and second thin water-vapor-permeable membranesheets attached to the projections on opposing faces of the flexibleseparator, the flexible separator holding the first and secondwater-vapor-permeable membrane sheets in a spaced-apart parallelrelationship, the panel stiffened by attachment of the membrane sheetsto the flexible separator, the projections formed to provide firstchannels operable for carrying a first flow between the flexibleseparator and the first and second water-vapor-permeable membrane sheetsin a first direction across each of the panels; and elongated spacersbetween the adjacent ones of the panels, the elongated spacers spacedapart from one another in the first direction such that the secondchannels comprise openings having widths 20 times or more a thickness ofthe panels; the panels stacked in a parallel spaced-apart relationshipto provide open second channels between adjacent ones of the panels, thesecond channels extending to carry a second flow through the heat andmoisture exchanger in a second direction transverse to the firstdirection; wherein adjacent ones of the panels are spaced apart from oneanother by distances that are less than a thickness of the panels, andthe flexible separator of each of the plurality of panels has a depththat is at least 110% of a height of the second channels.
 2. The heatand moisture exchanger according to claim 1 wherein the flexibleseparator of each of the plurality of panels has a depth that is in therange of 110% to 150% of a height of the second channels.
 3. The heatand moisture exchanger according to claim 1 wherein the flexibleseparator comprises a corrugated sheet.
 4. The heat and moistureexchanger according to claim wherein the flexible separator isperforated.
 5. The heat and moisture exchanger according to claim 1wherein each of the panels has a thickness in the range of 1.5 mm to 4mm.
 6. The heat and moisture exchanger according to claim 1 wherein theflexible separator comprises a formed aluminum sheet.
 7. The heat andmoisture exchanger according to claim 1 comprising a plurality ofvortex-generating features in at least the first channels or the secondchannels, the vortex-generating features comprising features selectedfrom: projections from and indentations into one or more surfacesbounding the first channels or the second channels.
 8. The heat andmoisture exchanger according to claim 1 comprising a plurality ofvortex-generating features in at least the first channels or the secondchannels, the vortex-generating features formed on one or both of thefirst and second water-vapor-permeable membrane sheets.
 9. The heat andmoisture exchanger according to claim 8 wherein the plurality ofvortex-generating features comprises an array of projections formed in asurface of at least one of the first or second water-vapor-permeablemembrane sheets, the projections having heights not exceeding thegreater of: 2 mm and 40% of a thickness of the flexible separator. 10.The heat and moisture exchanger according to claim 1 wherein the firstand second water-vapor-permeable membrane sheets are asymmetrical andcomprise a substrate having an air-impermeable, water-vapor permeablecoating on one face of the substrate, wherein the first and secondwater-vapor-permeable membrane sheets are oriented such that thecoatings face into the second channels.
 11. A panel according to claim 3wherein the flexible separator comprises a formed aluminum sheet.